Light-diffusing body and method of producing same



I06. COMPOSiTIONS,

COATING 0R PLAST'C .45 Patented Apr. 15, 1941 UNITED STATES PATENT CrossReference OFFICE LIGHT-DIFFUSING BODY AND METHOD OF PRODUCING SAMEJersey No Drawing. Application August 9, 1938,

Serial 223,854 7 SCIaims M This invention relates to the coating ofhollow glass bodies or hollow vitreous articles such as incandescentelectric lamp bulbs or the like.

In the manufacture of electric incandescent lamps it has been recognizedfor some years.

that there are important advantages in providing a translucent orfrosted bulb. Included among these advantages are the reduction of glareof the incandescent filament and the diffusion of the light emanatingtherefrom. Various methods have been employed to render the bulblight-diffusing; for instance, a common method of accomplishing thisresult is to frost the glass either inside or outside by means of anetching fluid, or the bulb may be made either partially or wholly of anopal glass, or a coating of light-diffusing nature may be applied eitherto the inside or to the outside of the bulb.

The production of good light-diffusing bulbs has become increasinglyimportant with the increased efficiency rating of lamps at presentmanufactured. For instance, a 60 watt lamp at first had an efliciency of11.6 lumens per watt, whereas a lamp of this same wattage now has anefficiency of 13.97 lumens per watt, the increased efficiency being inthe main due to the use of filaments, notably tungsten, whichconcentrate the light source to a relatively small space. Because of theincreased intensity and concentration of the light source, bulbshitherto designed or treated to produce translucent lightdifiusingsurfaces are now inadequate properly to diffuse the light. The result isthat such lamps manifest a very considerable amount of the verylocalized brightness and glare which present methods of frosting orcoating, or making of opalescent glass, were originally designed toeliminate.

Opal glass is very expensive and has not been found to be practicable inthe quantity production of electric incandescent lamp bulbs. Frosting byetching requires great care in controlling the action of the etchingfluid, and invariably results in a bulb considerably weaker than aclear, unfrosted bulb.

Moreover, no satisfactory method has hitherto been devised to coat theinside of lamp bulbs of all types and wattages. It has not hitherto beenpractical to coat gas-filled lamps of the kind known in the industry astype C or gasfilled incandescent lamps, and even in the case of vacuumlamps it has been found unsatisfactory to coat lamps larger than 40 wattsize. It is true that gas-filled lamps are on the market which have aninside coatin on the round of g s-a...

the bulb only, but such lamps must be burned I in a position with thebase upward in order to avoid rapid blackening and unduly short life.

It is an object of the present invention to provide a lamp with anefiicient and lasting inside coating of light-diffusing characten'and aprocess for applying this coating. The lamps of the invention may rangefrom the smallest sizes to the largest of 300 watts or larger, and theselamps may be either the vacuum type or gas-filled, and may be burned inany position required by ordinary fixtures, without undue blackeningwithin the normal commercial life of the lamp.

In applying the invention, a white light-diffusing coating is firstprepared having approximately the following formula:

Li iopo grams 575 20 SoWof sodium silicate in distilled water-(specificgrav1ty of sol'fitio'lf' Another satisfactory formula is as follows:

Bar hate grams.. 800

Solution of sodium silicate in distilled water, speci c gravi y o .014,the ratio of si'l'i'ca to soda being 3.22 to 1 cc.. 2400 It is veryimportant that the aqueous component of the sodium silicate solutionshould be free from foreign mineral content, and for this reason it ishighly advantageous not to use ordinary tap water but to distiltHFWEtEFWhich entersififithe composition of the coating material. Thepresence of even small quantities of minerals or acids seriously affectsthe color of the coating and may produce other undesirable effects.

The solid component of the coating, which may be some othernon-volatile, refractory, substantially insoluble, water-free, finelydivided solid pigment, such as titanium oxide, barium sulphate, orcombinations of titanium oxide and 5ar1umsulpfiate, or of titanium oxideand lithopone myst b c; very pure. Materials of this type s ould bechemical! ure or rea ent ure. They should E free from any appreciableamounts of water, substances containing water, substances, as solublesalts, which will unite or combine with water, or substances which willcombine with other materials to give off water or other undesirablevolatile compounds that might subsequently be freed in a lamp during thetime the filament is incandescing.

Further, the ratio of silica to soda of the Examiner 8 QOAHNG R PLAsHu mU HUIUI UIICB sodium silicate should be relatively high so that theworking and drying qualities of the liquid coating material areenhanced. Such ratio may vary between 3.22 and 3.86 of silica to gne ofsoda-that is, or eadh par 0 so um o e mo) there will be 3.2 parts ofsilicon oxide (SiOz).

The concentration of the sodium silicate is also highly important.Sodium silicate of a gravity of 1.01, for instance, results in a lampwhich has undesirable swirling markings in the coating due to the actiontaking place within the bulb during exhaust. On the other hand. ifsodium silicate of a specific gravity of 1.02 is used, the glass bulb isrendered so brittle that it breaks under very slight shocks. At theconcentration mentioned in the formula, namely, specific gravity of1.014, and the silica soda ratio of 3.22 to 1, neither of theseundesirable results are efiected.

. The foregoing briefly outlines the various requirements for coatingmaterials best suited for use in the process of the invention. Suchcoating materials are particularly described and claimed in anapplication of Walter E. Koemer, filed concurrently herewith.

An illustrative method of coating bulbs by utilizing the foregoin typeof coating composition proceeds as follows: The clear bulbs are firstheated in an oven at an oven temperature of approximately 200 C. Thebulbs remain in this oven from one to two minutes. The bulbs are thensprayed by means of a spray gun of well known type, the air used in thisgun being pre-filtered and pre-dried. The filtering of the air iscarried out with great care to separate and remove all traces ofmoisture, oil, and other foreign substance. Due to this filtering andheating, and to the fact that the coating is applied while the bulbs arestill hot from the pre-heating, the coating material is partiallydehydrated when it settled on the inner surface of the pro-heated bulbs.It is also important that the atomizin gun be brushed each time thespraying operation is interrupted, with a solution of C. P. sodiumhydroxide in distilled water, in order to remove from the nozzle of thegun any coating material which may have hardened thereon.

An important step in the process follows. When the bulbs are coated asabove described, they are aged for a period of at least 48 hours at roomtemperature. It is believed that a natural drying of the coating takeseffect in this manner with practically total elimination of moisture orwater vapor. If this drying effect were -sought by artificial heating atthis stage of the process, a shell of coating material would form thatwould imprison a great deal of the moisture which later, during theoperation of the lamp, would be released into the bulb with deleteriousefiects upon the filament and coating.

While we have stated that the above-mentioned aging treatment is carriedout for a period of at least 48 hours, at room temperature, it should beunderstood that conditions of humidity have an important bearing on thetime of drying. During humid days the drying time may have to beextended, whereas on dry days it may be shortened.

We may, however, desire to effect more constancy in drying time byconditioning the air so that proper drying conditions are obtained.

The next step is accomplished at the time the mounts are sealed into thebulbs. Just previous to sealing in, the sprayed bulbs are baked at anoven temperature of 350 C. and the bulbs are kept in this oven at thisoven temperature from one to two minutes depending upon the size of thebulbs. During this heating, dry filtered air is blown into the bulbs tofacilitate better circulation of the hot air within the bulbs and alsoto eliminate water vapor as fast as it is released. The bulbs are thensealed in and exhausted and during this step the temperature on thesealing-in machines and exhaust ovens should be increased to about 400to 450 C. in order to remove the last traces of moisture. Thetemperature employed in this step should be greater than that employedon the sealing-in and exhausting of the clear glass bulb or bulbsinside-frosted by etching, as the coating on the inside of the bulbs ofthis invention acts as a heat insulator and requires a greater heat topenetrate to the glass to drive out the water vapor.

Instead of sealing the lamp directly after drying and exhausting asabove outlined, we may fill the same with nitrogen or other suitable gasin order to produce a gas-filled, instead of a vacuum yp mp;

What we claim is:

1. The method of producing a light-diffusing coating on the interiorsurface of a hollow, vitreous body which comprises preheating and dryingsaid surface at an oven temperature of 200 C., depositing thereon acoating material consisting of a pigment incorporated in a solution ofsodium silicate in distilled water, said solution having a specificgravity of 1.014, drying said applied coating at room temperature for aperiod of at least 48 hours, baking and further drying said coated bodyat an oven temperature of approximately 350 C., and finally hermeticallysealing and exhausting said body at a temperature of 400 to 450 C.

2. The method of producing a light-diffusing coating on the interiorsurface of a hollow vitreous body which comprises preheating and dryingsaid surface, depositing thereon a coating material consisting of apigment incorporated in a solution of sodium silicate in distilledwater, said solution having a specific gravity of 1.014, drying saidapplied coating at room temperature for a period of approximately 48hours, and finally heating, air-drying, hermetically sealing andexhausting said body at elevated temperatures.

3. The method of making light-diffusing incandescent electric lampswhich comprises preheating and drying the interior of vitreous bulbs,coating the said interior surface with a coating material consisting ofa pigment incorporated in a solution of sodium silicate in distilledwater, said solution having a specific gravity of 1.014, drying saidapplied coatin at room temperature for a period of approximately 48hours, heating and further drying said coated bulb at elevatedtemperature, sealing a mount in said bulb, and finally exhausting saidbulb and sealing the exhaust tube thereof at a temperature of 400 to 450C.

4. The method of making light-diffusing incandescent electric lampswhich comprises preheating and drying the interior of vitreous bulbs,

coating the said interior surface with a coating material consisting ofa pigment incorporated in a solution of sodium silicate in distilledwater, said solution having a specific gravity of 1.014, drying saidapplied coating at room temperature for a period of approximately 48hours, heating and further drying said coated bulb, and finally formingthe same into a lamp at a temperature of 400 to 450 C.

5. The method of making light-diffusing incandescent electric lampswhich comprises preand then quickly at elevated temperature, and heatingand drying the interior of vitreous bulbs, finally forming the same intoa lamp at elevated coating the said interior surface with a coatingtemperature.

material consisting of lithopone incorporated in WALTER E. KOERNER.

a solution of sodium silicate in distilled water, said 5 ALFRED F.BAHLKE. solution having a specific gravity of 1.014, drying STUART F.MARVIN.

said coated bulb first slowly at room temperature

